var li = document.getElementById('themes').getElementsByTagName("li");//这里返回的是多个，getElements很明显复数嘛
    // console.log(li[0]);
    for(i=0;i<li.length;i++){
    	(function(i){
    		li[i].onclick = function(){
    			if(i==0){
			    	document.body.style.backgroundColor="#2b3546";
			    	document.getElementById('topcolor').style.backgroundImage="url('image/sky1.png')";
			    	document.getElementById('backpic').style.backgroundImage="url('image/water.png')";
			    	document.getElementById('sayhi').style.color="white";
			    }
			    else{
			    	document.body.style.backgroundColor="#b7ecf1";
			    	document.getElementById('topcolor').style.backgroundImage="url('image/sky2.png')";
			    	document.getElementById('backpic').style.backgroundImage="url('image/leaf.png')";
			    	document.getElementById('sayhi').style.color="#4f8696";
			    }
    		}
    	})(i)
    }